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a function to find the fastest DNS server
http://public-dns.info gives a list of online dns servers. you need to change the country in url (br in this url) with your country code. this command need some time to ping all IP in list.

dmesg with colored human-readable dates
Use sed to color the output of a human-readable dmesg output

Delete empty, 24-hours-old directories recursively, without consider hidden directories

Averaging columns of numbers
This example calculates the averages of column one and column two of "file.dat". It can be easily modified if other columns are to be averaged.

Port Knocking!
Knock on ports to open a port to a service (ssh for example) and knock again to close the port. You have to install knockd. See example config file below. [options] logfile = /var/log/knockd.log [openSSH] sequence = 3000,4000,5000 seq_timeout = 5 command = /sbin/iptables -A INPUT -i eth0 -s %IP% -p tcp --dport 22 -j ACCEPT tcpflags = syn [closeSSH] sequence = 5000,4000,3000 seq_timeout = 5 command = /sbin/iptables -D INPUT -i eth0 -s %IP% -p tcp --dport 22 -j ACCEPT tcpflags = syn

Delete an IPtable rules based on row number

convert a pdf to jpeg
Converts a .pdf to .jpg . should work with jpeg | tiff | png | gif | jp2 | pict | bmp | qtif | psd | sgi | tga

create a simple version of ls with extended output
create a short alias for 'ls' with multi-column (-C), file type syntax additions (slashes after directories, @ for symlinks, etc... (-F), long format (-l), including hidden directories (all ./, ../, .svn, etc) (-a), show file-system blocks actually in use (-s), human readable file sizes (-h)

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

check open ports without netstat or lsof


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